Hay Jeff,
Your local Hobby store should have these in stock (?), just get one off / for a 3905 or and REVO 3.3 and you'll be good to go!, they are all the same part or jump on E-Bay and get them.
Stock replacements:
http://cgi.ebay.com/NEW-TRAXXAS-T-MA...QQcmdZViewItem
http://cgi.ebay.com/NEW-E-REVO-AXLE-...QQcmdZViewItem
http://cgi.ebay.com/Traxxas-E-Revo-N...QQcmdZViewItem
hope that helped (?) have a great one
Shaun.